The purpose of this project is to develop a computer simulation of the kidney, which describes transport of electrolyte, nonelectrolyte and water in both steady state and tranient behavior. Current work is directed toward the development and theoretical analysis of efficient numerical methods of solving the differential-integral equations describing the renal counterflow system and of estimating model paramters. BIBLIOGRAPHIC REFERENCES: Tewarson, R. P., Stephenson, J. L., Kydes, A. and Mejia, R. Use of sparse matrix techniques in numerical solution of differential equations for renal counterflow systems. Computers and Biomedical Research, 9:507-520, 1976. Mejia, R., Kellogg, R. B., Stephenson, J. L., Comparison of numerical methods for renal network flows. J. Comp. Phys., 23:53-62, 1977.